"We want to know what PetroVietnam's social responsibilities will be," the letter, in Spanish, reads. "How will the local population benefit from oil extraction?"

The letter was given to Humala on 14 July in Santa Clotilde, a town on the River Napo, and was signed by, among others, the mayor, the district governor, the parish church and Catholic mission, the president of indigenous organization FECONAMNCUA, and other civil society representatives. That letter was followed shortly by another exactly a week later, this time signed by the presidents of FECONAMNCUA and another local indigenous organization, ORKIWAN, together representing 73 indigenous communities, which raises similar concerns and names two other oil companies, SubAndean and Petrobras, in addition to Perenco, Repsol-YPF and PetroVietnam.

"The companies' presence is a constant worry for the indigenous peoples living in the Napo basin,' the second letter reads. 'These last few years they have been operating have seen no real benefits for the local population: we're always the last to be heard, despite what the law says."

On the lack of indigenous land title the second letter reads, 'Our territory is being invaded by illegal, informal companies endangering the forest, which has been divided up, without consultation, to foreigners for exploitation and abuse.'

Most vulnerable of all are the 'isolated' indigenous groups who live in the most remote parts of the Napo region. They have no regular contact with other people, including other indigenous people, and could easily be decimated if contact is made with company workers.